Each entity could have multiple components. These are usually representing concepts such as Security Groups, ACLs and RouteTables.
Components don't show directly in the diagram as they are an extension to a resource's metadata.
Clicking on a component for a resource such as a Subnet (shown) will launch a full-screen slideout with data about the component:
Using the 'Associated' tab you can see all resources that are associated with this component. You can also create a diagram view that is specific to an individual component by clicking the 'Show in Diagram' button.